In catalytic converters for automotive vehicles catalysts are supported on substrates having a large area and exhaust flow passages over the area so that intimate contact between the exhaust gas and the catalyst can occur. Honeycomb substrates formed of foil strips have been proposed but they are typically deficient in some respect and/or present problems from a manufacturing and/or functional standpoint. For example, it is known to form the honeycomb substrate by spirally winding strips of smooth and corrugated foil but there results the problem of relative telescoping or sliding between the layers which first abrades the catalyst and can end in structural failure. With such an arrangement, it is difficult to maintain the integrity of the metal substrate without some form of mechanical strengthening or bonding of the layers. Then there remains another major problem of allowing design flexibility in the shape of the metal-layered substrate cross-section to meet various space allocations while maintaining a curved profile for housing strength reasons. This is particularly important in meeting certain vehicle under-floor space requirements where a low profile cross-section of, for example, oval shape is desired over a circular one which requires a larger height for the same frontal area. Moreover, there is the difficulty and expense of manufacture in completely forming a metal-layered substrate so as to be suitable for a final step of applying the catalyst coating.
There have been several proposals for containing the corrugated foil in the desired profile using some form of welding, brazing or mechanical retention. The latter approach is disclosed by U.S. Pat. Nos. 4,619,921 and 4,559,205 assigned to the assignee of the present invention. In both of these patents alternating layers of smooth foil and corrugated foil of varying widths are stacked to achieve the desired oval profile and then are sheathed in a retainer comprising a pair of metal shells which are assembled by pressing them over the foil layers and then welding the shells together at their mating plane. The patents described below utilize welding of the foil. U.S. Pat. No. 4,186,172 shows a spirally wound structure of circular cross-section having alternating smooth and corrugated sheets. The welding is done by laser beam or electron beam welders either during the winding process or after winding. U.S. Pat. No. 4,282,186 also shows a spiral wound structure but which has a hollow center so that it may be flattened to form an oval racetrack profile. Spot welds are made in the end faces of the foil matrix by electron beam; or brazing of the end faces may be used instead. In another version, instead of welding the end faces of the foil, semi-elliptical half-shells are pressed around the matrix and welded together to maintain the oval shape.
It is known to form chevron patterns in metal foil sheets and to stack the sheets into assemblies having a large surface area for supporting catalysts and having gas flow passages to promote contact of the exhaust gas with the catalyst. U.S. Pat. No. 4,382,323, assigned to the assignee of the present invention, shows such a chevron pattern foil wound in a spiral but the manner of retaining it in a wound shape is not disclosed. Ridges in the adjacent layers of the foil abut and cross one another at their peaks to form passages between the sheets. U.S. Pat. No. 4,753,919 discloses a method for optimizing the number of contact points between confronting surfaces of an accordion folded metal foil corrugated in a chevron pattern by specifying a certain mathematical relationship of the chevron and foil dimensions. The manner of securing the layers of the stack is not discussed.